Project Summary/Abstract Stimulus-inducible gene transcription ties changes in neuronal activity to the adaptations of neuronal and synaptic function that underlie long-lasting, environmentally-induced changes in circuit dynamics. Epigenomic modifications of chromatin, including histone acetylation, are proposed to regulate this process by tuning the likelihood or magnitude of gene transcription. In the Nucleus Accumbens (NAc), the psychostimulant-inducible gene Fosb is critical for generating the long-term cellular plasticity underlying addictive-like behavior, and histones at its promoter are acetylated in response to psychostimulant exposure. It remains unknown, however, whether the regulation of histone acetylation is causative for psychostimulant-induced changes in FosB expression and the development of addictive-like behaviors. This proposal will utilize a novel strain of CRISPR/dCas9 transgenic mice to directly alter the chromatin landscape at the Fosb promoter through delivery of the acetyltransferase enzymatic core domain of p300 (dCas9-p300core), which increases acetylation in the targeted region. Our previous data show that editing histone acetylation leaves the temporal stimulus- dependent expression of inducible genes intact, while augmenting or depressing the amplitude of induced gene expression. Thus, we can use this epigenome editing method to assess the specific functions of stimulus regulation of Fosb in vivo. Aim 1 will utilize in vivo drug exposure paradigms known to produce heightened Fosb expression in specific cell populations of the Nucleus Accumbens to test the hypothesis that delivery of p300 to the Fosb promoter enhances Fosb expression preferentially in the activated cell ensemble. Aim 2 will test how acetylation at the Fosb promoter affects sensitivity to the locomotor and rewarding properties of psychostimulants. Taken together, these data will develop a novel experimental approach that can be used to assess the mechanisms by which epigenetic regulation of psychostimulant-inducible genes modulates the development of addictive-like behaviors.